1. Field of the Invention
The invention relates to gas turbines, and more particularly to a system for igniting the fuel-air mixture in the combustion chamber of a gas turbine at high altitude in which environment combustion is sometimes difficult to initiate due to lack of oxygen, transient disturbances in the flow of working fluid, depressed temperatures, etc.
2. Description of the Prior Art
A number of attempts have been made to solve the aforementioned problem. For example, Johnston U.S. Pat. No. 3,330,985 discloses an igniter wherein gas flows internally thereof between a central solid electrode and a surrounding tubular electrode to cool the electrodes and enhance projection of the spark arc. However, this technique precludes the use of surface gap spark plug having a semi-conductor bridging the gap between the electrodes. Moreover, high velocity gas flow through the arc introduces the possibility of spark blow out.
Similarly, the patent to Harkness et al U.S. Pat. No. 2,465,092 teaches flow of air between the electrodes across the spark gap. Both of the aforesaid teachings have the potential liability that fluid flow through the arc may extenguish the arc rather than enhancing spark promulgation.
The patent to Morishita U.S. Pat. No. 4,215,979 teaches the induction of pressurized air into an annulus between an igniter and a shroud where it is admixed with pressurized gaseous fuel. The Morishita device functions to produce a turbulent mixture of air and fuel for introduction to the arc drawn by the igniter.
The patent to DeCorso U.S. Pat. No. 2,784,553, like Morishita, blows an air-fuel mixture past an igniter to effect ignition of said mixture which torches into the combustion chamber.
The patent to Lentz U.S. Pat. No. 2,831,993 discloses a shrouded igniter wherein air is inducted into a passage surrounding the igniter to effect cooling thereof under certain conditions. Lentz is useful only for a teaching that airflow patterns are capable of blowing an air-fuel mixture away from the area wherein ignition occurs.